ISO/IEC 15415 Grading Parameters
The ISO/IEC 15415 standard specifies those measuring, evaluating, and grading methods and parameters, which determine the quality of 2D symbols, and identifies possible causes of symbol errors.
Unused Error Correction (UEC) is the percentage of the error correction capability that is available for additional incorrect modules. The assignment of grade is according to the following table:
| UEC % | Grade |
|---|---|
| 62 ≤ x | A (4.0) |
| 50 ≤ x < 62 | B (3.0) |
| 37 ≤ x < 50 | C (2.0) |
| 25 ≤ x < 37 | D (1.0) |
| x < 25 | F (0) |
Symbol Contrast (SC) represents the difference in reflectivity between the brightest module and the darkest module of the 2D code. Based on the difference a grade is assigned according to the following table:
| SC% | Grade |
|---|---|
| 70 ≤ x | A (4.0) |
| 55 ≤ x < 70 | B (3.0) |
| 40 ≤ x < 55 | C (2.0) |
| 20 ≤ x < 40 | D (1.0) |
| x < 20 | F (0) |
Modulation (MOD and RM) is a grade based on the amount of variability in reflectivity of the modules of the 2D code. A multi-step process is used to get the modulation grade.
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First, the reflectivity of each module is compared to the global threshold and the overall symbol contrast according to the formula:
MOD = 2 * (abs(R - GT)) / SC
The Global Threshold GT is the midpoint between the reflectance of the brightest module and the reflectance of the darkest module.
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Next, the grade level for each module is determined from the MOD value according to the following table:
MOD % Grade 50 ≤ x A (4.0) 40 ≤ x < 50 B (3.0) 30 ≤ x < 40 C (2.0) 20 ≤ x < 30 D (1.0) x < 20 F (0)
The value of the grade for the Modulation parameter is the highest modulation level for which the modules meeting that level result in a theoretical Unused Error Correction grade of that level or higher. The module with the lowest MOD is reported as Contrast Uniformity (CU) in General Characteristics to facilitate conformance testing to the requirements of ISO/IEC 15426-2.
The RM parameter works in a similar way, except that for modules which are corrected as errors by the error correction, the MOD% is taken as 0 and counts as F in the final evaluation of the Modulation parameter grade according to the notional Unused Error Correction grade.
Axial Non-uniformity (ANU) represents the amount of “out of square” the modules are, that is, a measure of the overall aspect ratio of the symbol. For rectangular symbols which are not square, the ANU parameter reports the deviation from the aspect ration of a square which the ANU considers "correct"..
| ANU % | Grade |
|---|---|
| x ≤ 6 | A (4.0) |
| 6 < x ≤ 8 | B (3.0) |
| 8 < x ≤10 | C (2.0) |
| 10 < x ≤ 12 | D (1.0) |
| 12 < x | F (0) |
Grid Non-uniformity (GNU) is the worst-case distance between the calculated center of a module and the ideal location for the center of the module based on perfectly evenly spaced modules. The calculated center of the module is determined using clock track edges in accordance with the reference decode algorithm. The value is reported as a percentage of a module size.
| GNU % | Grade |
|---|---|
| ≤ 38 | A (4.0) |
| 38 < x ≤ 50 | B (3.0) |
| 50 < x ≤ 63 | C (2.0) |
| 63 < x ≤ 75 | D (1.0) |
| 75 < x | F (0) |
Fixed Pattern Damage (FPD) is the overall grade for all the fixed pattern components. This grade is equal to the lowest grade of all the components listed.
The following is a list of components of the finder pattern for Data Matrix symbols. For QR Code symbols, the parameters described in ISO 18004 QR Code Grading Parameters are applicable, see ISO 18004 QR Code Grading Parameters.
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LLS (Left ‘L’ Side) is a grade based on imperfections in the left ‘L’ side of the finder pattern. There are two checks required to pass.
First requirement:
- Stretch of 4 correct modules separate gaps
- Gaps are made up of 3 modules or less
Second requirement:
- Grade assigned according to the table is not fail.
- The grade is calculated by the percentage of correct modules
- BQZ (Bottom Quiet Zone) is a grade based on imperfections in the quiet zone, which is a one-module area below the bottom ‘L’ side.
- BLS (Bottom ‘L’ Side) is a grade based on imperfections in the bottom ‘L’ side of the finder pattern (see Left ‘L’ Side).
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LQZ (Left Quiet Zone) is a grade based on imperfections in the quiet zone, which is a one-module area to the left of the left ‘L’ side. The grade is based on the percentage of modules, which are correct using the same grading table as for the ‘L’ sides.
% of incorrect modules Grade 0 A (4.0) 0 < x ≤ 9 B (3.0) 9 < x ≤ 13 C (2.0) 13 < x ≤ 17 D (1.0) 17 < x F (0) The LQZ grade is the highest modulation level in which the first (gap test) passes and the correct module percentage results in a grade of that level or higher.
- TQZ (Top Quiet Zone) is a grade based on imperfections in the quiet zone, which is a one-module area above the Top Clock Track.
- ULQZ (Upper Left Quiet Zone) is the top quiet zone above the upper left quadrant. Used only for 2 and 4 quadrant symbols, this is the grade based on the segment of the quiet zone above the top clock track of the left quadrant.
- URQZ (Upper Right Quiet Zone) is the top quiet zone above the upper right quadrant. Used only for 2 and 4 quadrant symbols, this is the grade based on the segment of the quiet zone above the top clock track of the right quadrant.
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RQZ (Right Quiet Zone) is a grade based on imperfections in the quiet zone, which is a one-module area to the right of the Right Clock Track.
- RUQZ (Right Quiet Zone to the right of the upper right quadrant): Only for 2 and 4 quadrant symbols, this is the grade based on the segment of the quiet zone to the right of the upper right quadrant.
- RLQZ (Right Quiet Zone to the right of the lower right quadrant): Only for 4 quadrant symbols, this is the grade based on the segment of the quiet zone to the right of the lower left quadrant.
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TTR (Top Transition Ratio) is a grade based on imperfections in the Top Clock Track, with relation to its adjoining quiet zone. Since the number of transitions in the quiet zone is zero, the ideal value for this parameter is zero. As the number of teeth in the clock track increases (larger symbols), more transitions in the quiet zone can be tolerated. More transitions in the clock track, which are really imperfections, also improve Top Transition Ration. The grading scheme for this transition ratio is:
Transition Ratio % Grade x ≤ 6 A (4.0) 6 < x ≤ 8 B (3.0) 8 < x ≤ 10 C (2.0) 10 < x ≤ 12 D (1.0) 12 < x F (0) - ULQTTR (Transition ratio for Upper Left Quadrant Top Clock Track): Only for 4 quadrant symbols, this is the grade based on the clock track segment at the top of the upper left quadrant. For a 2 quadrant symbol, this is labeled LQTTR.
- URQTTR (Transition ratio for Upper Right Quadrant Top Clock Track): Only for 4 quadrant symbols, this is the grade based on the clock track segment at the top of the upper right quadrant. For a 2 quadrant symbol this is labeled RQTTR.
- LLQTTR (Transition ratio for Lower Left Quadrant Top Clock Track): Only for 4 quadrant symbols, this is the grade based on the clock track segment at the top of the lower left quadrant.
- LRQTTR (Transition ratio for Lower Right Quadrant Top Clock Track): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment at the top of the lower right quadrant.
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RTR (Right Transition Ratio): Transition ratio for the right clock track in relation to the right quiet zone
- ULQRTR (Transition ratio for Upper Left Quadrant Right Clock Track): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment to the right of the upper left quadrant. For a 2 quadrant symbol, this is labeled LQRTR
- URQRTR (Transition ratio for Upper Right Quadrant Right Clock Track): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment to the right of the upper right quadrant. For 2 quadrant symbols, this is labeled RQRTR.
- LLQRTR (Transition ratio for Lower Left Quadrant Right Clock Track): Only for 4 quadrant symbols, this is the grade based on the clock track segment to the right of the lower left quadrant.
- LRQRTR (Transition ratio for Lower Right Quadrant Right Clock Track): Only for 4 quadrant symbols, this is the grade based on the clock track segment to the right of the lower right quadrant.
- TCT (Top Clock Track) is a grade based on imperfections in the top clock track. Some imperfections in the clock track can be tolerated. As a rule maintaining for a passing grade is that three out of every five modules on a consecutively rolling window of five modules must be correct. The value of the grade is the highest modulation level for which this test passes.
- ULQTCT (Top Clock Track for Upper Left Quadrant): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment at the top of the upper left quadrant. For 2 quadrant symbols this is labeled LQTCT.
- URQTCT (Top Clock Track for Upper Right Quadrant): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment at the top of the upper right quadrant. For 2 quadrant symbols this is labeled RQTCT.
- LLQTCT (Top Clock Track for Lower Left Quadrant): Only for 4 quadrant symbols, this is the grade based on the clock track segment at the top of the lower left quadrant.
- LRQTCT (Top Clock Track for Lower Right Quadrant): Only for 4 quadrant symbols, this is the grade based on the clock track segment at the top of the lower right quadrant.
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RCT (Right Clock Track) is a grade based on imperfection in the right clock track. Some imperfections in the clock track can be tolerated. As a rule maintaining for a passing grade is that three out of every five modules on a consecutively rolling window of five modules must be correct. The value of the grade is the highest modulation level for which this test passes..
- ULQRCT (Right Clock Track for Upper Left Quadrant): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment to the right of the upper left quadrant. For 2 quadrant symbols, this is labeled LQRCT.
- URQRCT (Right Clock Track for Upper Right Quadrant): Only for 2 and 4 quadrant symbols, this is the grade based on the clock track segment to the right of the upper right quadrant. For 2 quadrant symbols, this is labeled RQRCT.
- LLQRCT (Right Clock Track for Lower Left Quadrant): Only for 4 quadrant symbols, this is the grade based on the clock track segment to the right of the lower left quadrant.
- LRQRCT (Right Clock Track for Lower Right Quadrant): Only for 4 quadrant symbols, this is the grade based on the clock track segment to the right of the lower right quadrant.
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AG (Average Grade of Damage across many parts of the Finder Pattern) is a grade that considers the accumulated effect of damage to several parts of the finder pattern. Five values are averaged together. One of these is the lowest of all the grades associated with all the clock track segments, namely TCT, TTR, TQZ and RCT, RTR, RQZ. The other four are LLS, BLS, LQZ, and BQZ. The average falls in the range of 0 through 4.0 and is given a grade according to the following:
Ave Grade Grade Equals 4.0 A (4.0) 3.5 ≤ x < 4.0 B (3.0) 3.0 ≤ x < 3.5 C (2.0) 2.5 ≤ x < 3 D (1.0) x < 2.5 F (0)
DECODE: Reports whether the 2D Symbol is decoded in accordance with the reference decode algorithm with the specified aperture.
It is possible to report decoded results, but for a failure to occur when decoding in accordance with the reference decode algorithm. In this case, the DECODE grade is F (0).
Contrast Uniformity (CU) is the value of MOD (modulation) for the worst-case module selected from a 2D Matrix symbol. This is useful for process control, as way of measuring the drift in reflectivity consistency, and for testing conformance to ISO/IEC 15426-2, which requires the modulation of a specific module within a conformance test symbol to be reported. This parameter is reported in General Characteristics.